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Topic: Alternator load with stereo system

in Forum: C3 Electrical

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Alternator load with stereo system (1/9)
7/25/10 11:54pm

Martins Vet
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Vette(s):
1980 Silver. Complete Edelbrock performer package. TRW rear spring, new shocks. New Firestone Firehawk tires, Shift kit

Joined: 5/16/2010
Posts: 14

Hi Everyone:

I was hoping a few of you might have run into this before.

I have a 1980 with a rebuilt 350 with with an Edelbrock Performer package. I am using the Marche under drive pulleys and have a hefty stereo system with amp and sub.

I have a replacement alternator (in it when I bought the car) and believe it is the 70 amp size that came with the car.

I have to keep my idle up at about 750 to 800 RPM so the choke and batt lights don't come on when sitting at idle. I also have a problem with the sub woofer cutting out when the volume is turned up while idling.

Any thoughts about replacing the alternator with a 100 amp unit? I don't want to fry anything. I am also considering adding a capacitor to the amp to help it cope with the current draw at idle.

Thanks in advance,

Martin

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Alternator load with stereo system (2/9)
7/26/10 12:48am

stingrayjim jr

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SHELBYVILLE, TN - USA

Vette(s):
1976 L48 auto

1978 L82 4speed

1994 LT1 6speed

Joined: 7/5/2002
Posts: 3942

Hey Martin, while i'm no electrical expert, might i ask just how large an amp are you using?... if i got my thinking right, if you have an underdive pulley system then the alternator will be turning slower than "usual"... meaning it might not be putting out a proper amount of amprage at idle, which would mean that a larger amp alternator will not really help much in this situation..? The capacitor will help with some of the issue with the amp, but, do be careful with those things. Maybe a standard pulley drive would help...? Also, do you have the amp wired straight to the battery?(considering its in the rear compartment, cable legnth shouldn't be an issue) and also do use a hefty size cable if your amp is 'hefty', like 1000 watt or higher... i run a 400 watt with 2 10 inch woofers, without much problem at all, and seems plenty loud enough, though i know there are louder ones out there, but, i'm not getting into crank off competitions :)

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StingrayJim
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Stingray's '76�� StingrayJr's '78��Lil Red '94

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Alternator load with stereo system (3/9)
7/26/10 12:27pm

Hi Jim:

I have a Mono subwoofer amplifier 400 watts RMS x 1 at 2 ohms - driving a 10 inch Sub.

I agree that an underdrive might be the culpret although it said in the instructions for the underdrive that it turns the alternator pully 25% faster to compensate for the main pully.

I dont use it for competition just once in a while when I am out alone or with my son we crank it to a good tune. Works fine while driving and the output of the alternator is charging, seems to be only while idling.

Thanks again,

Maritn

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Alternator load with stereo system (4/9)
7/26/10 5:12pm

cthulhu

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Hot Springs, AR - USA

Vette(s):
69 Conv #'s match 427, TKO-600/.64, 3.36HD-Posi, HT, T/T, PS, PB, PW, SP, Leather, Comp XE264HR & Roller Rockers & Lifters, Air-Gap RPM intake, Holley St Av 770 VS, MSD 6AL+Dist+Blaster SS, K&N, Jet-Hot Hooker Side-Pipes, Steeroids, Al Rad, Spal Fans

Joined: 4/24/2004
Posts: 3231

to get a capacitor large enough to make a difference you will spend some real money and take up some room but they do work.

here is a pretty good deal on a 5 farad Cap.

http://www.hifisoundconnection.com/Shop/Control/Product/fp/vpid/3920477/vpcsid/0/SFV/30046

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Alternator load with stereo system (5/9)
7/26/10 7:06pm

stingrayjim jr

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SHELBYVILLE, TN - USA

Vette(s):
1976 L48 auto

1978 L82 4speed

1994 LT1 6speed

Joined: 7/5/2002
Posts: 3942

one other thing i got to thinking about at work today was, how good of a condition is your battery?(oddly i didn't think of this earlier, as i work for a battery distributor(automotive)). If your battery is marginal, when the amp pulls a lot for the subwoofer to work, its obviously drawing enough voltage to cut itself off... not sure if you have "converted" your car's battery to a top post, or still using the side post connections, but you might want to make sure the connections are "sound" to the amp, and also make sure the battery is up to par :) WOW, a 5 farad cap? kinda scary...

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StingrayJim
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Stingray's '76�� StingrayJr's '78��Lil Red '94

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Alternator load with stereo system (6/9)
7/26/10 8:38pm

cthulhu

[QUOTE=stingrayjim] WOW, a 5 farad cap? kinda scary...[/QUOTE]

yeah it is on the big side... but many of the 1 farad caps are roughly the same price...

when i was in college i made a living installing 5000$ stereo's in 500$ cars and the 2x2F caps was a fixture.

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Alternator load with stereo system (7/9)
7/27/10 1:29pm

VetteSpecialties
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Mounds View, MN - USA

Vette(s):
70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe

Joined: 5/24/2007
Posts: 1031

I believe the capacitor is like an electric shock absorber. It absorbs peaks, and lets out a little when the voltage is too low, but nothing will keep up while you idle through a red light. I agree with the people who say to check the rest of the electrical system. Your battery should easily support a stereo like yours for a few minutes. I would bet either your battery is failing or the wiring other than the alternator output is not up to capacity.

Larry

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Alternator load with stereo system (8/9)
7/28/10 11:35pm

Thanks for your input, I am presently searching for a three wire 100 AMP alternator before I try the capacitor, not sure if there is such a beast!

Capacitors can be an issue with space and then if the battery does discharge and you have to boost it, it sounds like you have to disconnect the capacitor then recharge it slowely or there can be a big spark and potential problems.

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Alternator load with stereo system (9/9)
7/30/10 2:41pm

nosal1
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Dunedin, FL - USA

Vette(s):
1980 Corvette Torch Red with Gold metallic 370HP/350 CU.IN.Turbo 350 w/shift kit.Originally CA.Car with 305 CU.IN.

Joined: 3/21/2006
Posts: 262

Martins Vette,

There are a whole host of three wire and one wire Chromed Alternators available.I just put one on my '80 with and under drive pulley and works great and maintains at idle 13.6(checked by volt meter)and supports the stereo etc.even when AC is operating.

They are available through Jegs,Summit and Ebay.I usually to buy the cases from Jegs/Summit and change the internals to 100 AMP parts,however now it is cheaper to buy them on Ebay than rebuilding them myself...

Good luck and hunting..

Sal C nosal1

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